1. Field of the Invention
The invention relates to a chemical filter medium for filtering and removing chemicals, a chemical filter including the chemical filter medium, and a method of manufacturing the chemical filter. More particularly, the invention relates to a chemical filter medium employed in a clean room for removing chemical contaminants such as ozone or nitrogen oxide, a chemical filter including the chemical filter medium, and a method of manufacturing the chemical filter.
2. Description of the Related Art
Generally, minute devices such as semiconductor devices are manufactured in a clean room where contaminants having sizes larger than a critical size are removed. Particularly, the contamination level in the clean room greatly affects the throughput of a semiconductor device manufacturing process.
As semiconductor devices become more highly integrated using a wafer having large diameter, the contamination degree of the clean room should be precisely controlled because very minute contaminants in the clean room may cause failures in the operation of the semiconductor devices. Here, the minute particles in the clean room may include particles such as minute dust particles and chemical contaminants such as noxious gases.
The chemical contaminants in the clean room in which the semiconductor devices are manufactured are controlled using a chemical filter. The chemical filter generally removes noxious gases using impregnated activated carbon as a filter medium that collects the noxious gases. The impregnated activated carbon includes conventional activated carbon and metal, or metal salts impregnated on the surface and inner pores of the conventional activated carbon. With the metal or the metal salts, the impregnated activated carbon can have improved catalytic characteristics such as chemical activation and selective absorption relative to specific components. The chemical filter having the impregnated activated carbon as the filter medium effectively removes chemical contaminants generated in the clean room such as ozone or ammonia.
However, the chemical filter having the impregnated activated carbon as the filter medium may not remove nitrogen oxide and sulfur oxide that exist in the clean room in minute amounts. As the semiconductor devices have been highly integrated, minute quantities of nitrogen oxide or sulfur oxide in the clean room may cause the failure of the semiconductor devices. The nitrogen oxide or the sulfur oxide should be removed to prevent the failure of the semiconductor devices. To remove the nitrogen oxide and the sulfur oxide from the clean room, an additional chemical filter having a filter medium for removing the nitrogen oxide and the sulfur oxide is required.
As described above, the conventional chemical filter removes one contaminant or similar kinds of contaminants. Various contaminants are contained in an air introduced in the clean room so that various chemical filters are installed in the clean room as a multi-layered construction so as to remove these different contaminants. However, the space in the clean room for locating these chemical filters is insufficient. Moreover, there are significant costs for maintaining all of these various chemical filters.
To solve these problems, a chemical filter is preferably provided which removes two or three kinds of contaminants at the same time. Examples of this chemical filter having several filtering base materials as a filter medium are disclosed in the Japanese Laid Open Patent Publication 2001-300218, Japanese Laid Open Patent Publication 2001-276608 and Japanese Patent Laid Open Patent Publication No. 1999-319460.
FIG. 1 is a cross-sectional view illustrating an example of the conventional filter mediums disclosed in the above publications. Referring to FIG. 1, the conventional filter medium comprises a mixture of several filtering base materials such as activated carbon 10 or zeolite 12, and a resin, etc. However, this conventional chemical filter including the mixture of the filtering base materials may not have good overall contaminant removal efficiency. Generally, the conventional chemical filter including the mixture of filtering base materials has relatively high removal efficiency of ozone, but has poor removal efficiency of nitrogen oxide. Furthermore, the conventional chemical filter may hardly remove nitrogen monoxide.